Host specialisation and competition asymmetry in coleopteran parasitoids

Are some species ‘robust’ to exploitation? Explaining persistence in deceptive relationships

Animals and plants trick others in an extraordinary diversity of ways to gain fitness benefits. Mimicry and deception can, for example, lure prey, reduce the costs of parental care or aid in pollination–in ways that impose fitness costs on the exploited party. The evolutionary maintenance of such asymmetric relationships often relies on these costs being mitigated through counter-adaptations, low encounter rates, or indirect fitness benefits. However, these mechanisms do not always explain the evolutionary persistence of some classic deceptive interactions.

Sexually deceptive pollination (in which plants trick male pollinators into mating with their flowers) has evolved multiple times independently, mainly in the southern hemisphere and especially in Australasia and Central and South America. This trickery imposes considerable costs on the males: they miss out on mating opportunities, and in some cases, waste their limited sperm on the flower. These relationships appear stable, yet in some cases there is little evidence suggesting that their persistence relies on counter-adaptations, low encounter rates, or indirect fitness benefits. So, how might these relationships persist?

Here, we introduce and explore an additional hypothesis from systems biology: that some species are robust to exploitation. Robustness arises from a species’ innate traits and means they are robust against costs of exploitation. This allows species to persist where a population without those traits would not, making them ideal candidates for exploitation. We propose that this mechanism may help inform new research approaches and provide insight into how exploited species might persist.

Genomic Resources for Goniozus legneri, Aleochara bilineata and Paykullia maculata, Representing Three Independent Origins of the Parasitoid Lifestyle in Insects

Parasitoid insects are important model systems for a multitude of biological research topics and widely used as biological control agents against insect pests. While the parasitoid lifestyle has evolved numerous times in different insect groups, research has focused almost exclusively on Hymenoptera from the Parasitica clade. The genomes of several members of this group have been sequenced, but no genomic resources are available from any of the other, independent evolutionary origins of the parasitoid lifestyle. Our aim here was to develop genomic resources for three parasitoid insects outside the Parasitica. We present draft genome assemblies for Goniozus legneri, a parasitoid Hymenopteran more closely related to the non-parasitoid wasps and bees than to the Parasitica wasps, the Coleopteran parasitoid Aleochara bilineata and the Dipteran parasitoid Paykullia maculata. The genome assemblies are fragmented, but complete in terms of gene content. We also provide preliminary structural annotations. We anticipate that these genomic resources will be valuable for testing the generality of findings obtained from Parasitica wasps in future comparative studies.

Influence of Density on Interspecific Competition Between Spathius galinae (Hymenoptera: Braconidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae), Larval Parasitoids of the Invasive Emerald Ash Borer (Coleoptera: Buprestidae)

The outcomes of interspecific interactions between parasitoids depend on a variety of factors. Understanding the influence of these factors is important for classical biological control, where the success of parasitoid releases partly depends on interactions with native and other introduced species. However, results from laboratory experiments may not always reflect those in the field, as densities may be artificially inflated. To mitigate this problem, we examined the effects of multiple densities on interspecific competition between two larval parasitoids of emerald ash borer (Agrilus planipennis Fairmaire): Spathius galinae Belokobylskij and Tetrastichus planipennisi Yang. Parasitoid species were housed individually or together at two different densities, and we measured the effects on percent parasitism and progeny production, before calculating the interaction strengths. We found no significant effects of parasitoid density on percent parasitism, but the effect of competition on parasitism generally was reduced at lower densities. However, there were significant differences in parasitism by species, with S. galinae parasitizing more larvae than T. planipennisi. There were also no significant effects of parasitoid density on the number of progeny produced by each species, though the effect of competition on progeny production was greater at higher densities. Similarly, though, there were significant differences between species in the number of progeny produced. Specifically, T. planipennisi consistently produced larger broods than S. galinae. Our findings complement existing research suggesting that competition between these two species in the field will likely be negligible.

Community Sampling and Integrative Taxonomy Reveal New Species and Host Specificity in the Army Ant-Associated Beetle Genus Tetradonia (Coleoptera, Staphylinidae, Aleocharinae)

Army ant colonies host a diverse community of arthropod symbionts. Among the best-studied symbiont communities are those of Neotropical army ants of the genus Eciton. It is clear, however, that even in these comparatively well studied systems, a large proportion of symbiont biodiversity remains unknown. Even more striking is our lack of knowledge regarding the nature and specificity of these host-symbiont interactions. Here we surveyed the diversity and host specificity of rove beetles of the genus Tetradonia Wasmann, 1894 (Staphylinidae: Aleocharinae). Systematic community sampling of 58 colonies of the six local Eciton species at La Selva Biological Station, Costa Rica, combined with an integrative taxonomic approach, allowed us to uncover species diversity, host specificity, and co-occurrence patterns of symbionts in unprecedented detail. We used an integrative taxonomic approach combining morphological and genetic analyses, to delineate species boundaries. Mitochondrial DNA barcodes were analyzed for 362 Tetradonia specimens, and additional nuclear markers for a subset of 88 specimens. All analyses supported the presence of five Tetradonia species, including two species new to science. Host specificity is highly variable across species, ranging from generalists such as T. laticeps, which parasitizes all six local Eciton species, to specialists such as T. lizonae, which primarily parasitizes a single species, E. hamatum. Here we provide a dichotomous key along with diagnostic molecular characters for identification of Tetradonia species at La Selva Biological Station. By reliably assessing biodiversity and providing tools for species identification, we hope to set the baseline for future studies of the ecological and evolutionary dynamics in these species-rich host-symbiont networks.